Terminal multiplexer and method of constructing the terminal multiplexer

ABSTRACT

A terminal multiplexer is constructed in such a manner that it can be upgraded for adapting to a change in a transmission system. Line terminating equipment (LTE) having working high speed transmission lines and protection high speed transmission lines in 1:1, is constructed from such units as two sets of 10G interfaces responsible for interface with the high speed transmission lines, and SELH which selects a high speed transmission line for which multiplex conversion is performed in relation to low speed transmission lines When this LTE is to be upgraded to ADM adapted for 2-Fiber BLSR, the unit SELH is replaced with SWH which performs switching of signals in each time slot between a high speed transmission line and the low speed transmission lines. Upgrading during the system operation is possible by making signal interfaces with the outside common for SELH and SWH, and by making delay times between signal input and output coincide for various signals.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.08/884,137, filed Jun. 27,1997, hereby incorporated by reference nowU.S. Pat. 6,049,525.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a terminal multiplexer which performsmultiplexing and demultiplexing of digital signals between a pluralityof low speed transmission lines and a high speed transmission line in adigital communication network and relates to a terminal multiplexer suchas a channel rearrange equipment, for example ADM (Add DropMultiplexer), having a cross connect function.

2. Description of Related Art

As a transmission system using a terminal multiplexer which performsmultiplex conversion of signals between a plurality of low speedtransmission lines and a high speed transmission line, there is known asystem in which line terminating equipments (hereinafter, referred to as“LTE”) are connected in a point-to-point manner, perform time divisionmultiplexing of low speed signals received from a plurality of low speedtransmission lines to send them as high speed signals onto a high speedtransmission line, and perform demultiplexing of high speed signalsreceived from the high speed transmission line into a plurality of lowspeed signals to send the demultiplexed signals onto respective lowspeed transmission lines, as shown in FIG. 13A.

As a configuration for realizing automatic protection switching in atransmission system using such LTEs, there are known 1:1 configurationand 1:n configuration. In the 1:1 configuration, a set of two workinghigh speed transmission lines which transmit signals in oppositedirections to each other and a set of two protection (i.e., preparatory)high speed transmission lines which transmit signals in oppositedirections to each other are provided between the LTEs at both ends. Inthe 1:n configuration, between the LTEs at both ends, there are provideda plurality of working high speed transmission lines in sets of pairs,which transmit signals in the opposite directions to each other, and aset of two protection high speed transmission lines which are used incommon with the plurality of high speed transmission lines and transmitsignals in opposite directions to each other.

In the present description, working lines will be represented by thesymbol “W” (working), and protection lines will be represented by thesymbol “P” (Protection), Further, as for terminal multiplexer connectedbetween two other terminal multiplexers, one side of the two otherterminal multiplexers will be described as “West” and the other sidewill be described as “East”.

Now, in LTEs in 1:1 and 1:n configurations, when a problem arises in aworking high speed transmission line, automatic protection switching isperformed so that the high speed transmission line used for transmittingsignals is switched from the faulty one to a protection high speedtransmission line. As a method for out this switching, thebi-directional switching method and the uni-directional switching methodare known. In the bi-directional switching method, as shown in FIG. 13B,both of the two high speed transmission lines in the faulty set areswitched to two protection high speed transmission lines. In theuni-directional switching method, as shown in FIG. 18C, only the faultyhigh speed transmission line is switched to a line having the samedirection of transmitting signals as the faulty line out of theprotection high speed transmission lines.

Further, as a terminal multiplexer which performs multiple conversionbetween a plurality of low speed transmission lines and a high speedtransmission line, as shown in FIG. 14A, there is known an ADM whichperforms demultiplexing of some high speed signals received from thehigh speed transmission line (West side) into a plurality of low speedsignals to send them onto the respective low speed transmission lines,and performs time division multiplexing of the remaining high speedsignals received from the high speed transmission line and low speedsignals received from the low speed transmission lines to send themultiplexed signals onto the other high speed transmission line (Eastside), or performs similar operations in the reverse direction from theEast side to the West side.

As a configuration of a transmission system using such an ADM, there areknown a linear configuration in which ADMs are located between LTEs asshown in FIG. 14B, and a ring configuration in which a plurality of ADMsare connected in a ring shape with high speed transmission lines asshown in FIG. 14C.

As the linear configuration using ADMs, there are known twoconfigurations corresponding respectively to the above-described 1:1 and1:n configurations of LTEs. In the 1:1 linear configuration, as shown inFIG. 15A, on each of the West and East sides, there are provided a setof two working high speed transmission lines for transmitting signals inopposite directions to each other and a set of two protection high speedtransmission lines for transmitting signals in opposite directions toeach other. In the 1:n linear configuration, as shown in FIG. 15B, oneach of the West and East sides, there are provided a plurality ofworking high speed transmission lines in sets of two, transmittingsignals in opposite directions to each other, and a set of twoprotection high speed transmission lines which are used in common withthe plurality of high speed transmission lines and transmit signals inopposite directions to each other. Here, at the time of the automaticprotection switching of ADM in 1:1 and 1:n linear configurations,switching from the working high speed transmission lines to theprotection high speed transmission lines is performed on each of theWest and East sides, similarly to the above-described switching in LTEin 1:1 and 1:n configurations.

On the other hand, as the ring configuration in which ADMs are connectedin a ring shape, there have been proposed a 2 fiber configuration inwhich each pair of adjacent ADMs are connected with a set of two opticalfiber transmission lines transmitting signals in opposite directions toeach other, and a 4 fiber configuration in which each pair of adjacentADMs are connected with two sets of two optical fiber transmission linestransmitting signals in opposite directions to each other.

Further, as the 4 fiber ring configuration, there is known 4-Fiber BLSR(Bi-directional Line Switched Ring) in which, as shown in FIG. 16A, outof two sets of optical fiber transmission lines connecting each pair ofADMs, one set is used as working lines and the other set is used asprotection lines. As the 2 fiber ring configuration as shown in FIG.17A, there are known 2-Fiber UPSR (Uni-directional Path Switched Ring)and 2-Fiber BLSR. In 2-Fiber UPSR, optical fiber transmission linestransmitting signals in one rotational direction are used as workinglines and optical fiber transmission lines transmitting signals in theother rotational direction are used as protection lines, and switchingis performed for each path. In 2-Fiber BLSR, instead of setting aworking or protection line for each optical fiber transmission line,some time slots on each optical fiber transmission line are used asworking slots and the other time slots are used as protection slots.

Now, switching from working lines to protection lines at the time ofautomatic protection switching in 4-Fiber BLSR is illustrated in FIGS.16B and 16C. As shown, as the switching performed by ADMs adjacent to afaulty portion in 4-Fiber BLSR, there are two kinds of switching, i.e.,(1) switching from a set of working optical fiber transmission lines onthe side of the faulty portion to a set of protection optical fibertransmission lines on the side of the faulty portion (FIG. 16B), and (2)turning back of signal flows from a set of working optical transmissionlines on the opposite side to the faulty portion to a set of protectionoptical fiber transmission lines on the opposite side to the faultyportion (FIG. 16C), the former being called Span Switch, and the laterRing Switch.

FIG. 17B illustrates the switching from the working time slots to theprotection time slots at the time of automatic protection switching in2-Fiber BLSR, and FIG, 17C illustrates the switching from the workingpath to the protection path at the time of automatic protectionswitching in 2-Fiber UPSR.

As shown, switching in 2-Fiber BLSR is performed in such a manner thatADMs adjacent to a fault portion turn back signal flow in working timeslots of two optical fiber transmission lines on the opposite side tothe faulty portion into protection time slots of two optical fibertransmission on the opposite side to the faulty portion. In FIG. 17B, inthe case that time slots A-F of #1 optical fiber transmission lines andtime slots A-F of #2 optical fiber transmission lines are used asworking time slots, and time slots G-L of #1 optical fiber transmissionlines and time slots G-L of #2 optical fiber transmission lines are usedas protection time slots, ADM A, B adjacent to the faulty portion turnback signal flow in the time slots A-F of #1 optical fiber transmissionlines into the time slots G-F of #2 optical fiber transmission lies, andturn back signal flow in the time slots A-F of #2 optical fibertransmission lines into the time slots G-F of #1 optical fibertransmission lines.

Further, switching of 2-Fiber UPSR is performed as shown in FIG. 17C.Namely, each ADM transmits signals to other ADMs, using both the workingoptical fiber transmission lines and protection optical fibertransmission lines. In a normal condition, each ADM receives signalsfrom other ADMs through working optical fiber transmission line andprocesses them, and when it can not receive from a particular ADMthrough the working optical fiber transmission line, it receives signalsfrom that particular ADM through protection optical fiber transmissionline and processes them.

As described above, functions required for a terminal multiplexer varyaccording to LTE used in the 1:1 configuration, LTE used in the 1:nconfiguration, ADM used in the 1:1 linear configuration, ADM used in the1:n linear configuration, ADM used in 4-Fiber BLSR, ADM used in 2-FiberBLSR, and ADM used in 2-Fiber UPSR. Accordingly, LTEs or ADMs have,conventionally, been made as dedicated equipments for each particularconfiguration of transmission system.

Sometimes, it is desired to change a configuration of a transmissionsystem, for example, in order to make the transmission system advanceafter the start of its operation. For example, it may be desired that,in order to increase transmission capacity, a transmission system usingLTEs connected in 1:1 configuration in a point-to-point manner ischanged to a transmission stem using LTEs connected in 1:n configurationin a point-to-point manner, that a transmission system using LTEsconnected in 1:1 configuration in a point-to-point manner is changed to2-Fiber BLSR or 4-Fiber BLSR, in accordance with increase in connectedpoints.

Conventionally, however, each LTE or ADM is a dedicated equipment for atransmission system before change, and therefore, when configuration ofsuch a transmission system is to be changed, LTEs or ADMs should beexchanged, so that the burden of introducing equipments is large at thetime of changing the configuration of a transmission system. Further,when LTEs or ADMs are exchanged, a transmission system must be takendown once, and communication must be stopped.

On the other hand, in accordance with recent increase in transmissioncapacity of a transmission system, a multiplex conversion equipmentbecomes of large scale. Accordingly, for example, it is, now, difficultto construct a terminal multiplexer adapted for OC-192 optical carrier192 using an optical fiber transmission line with 10 G of transmissioncapacity as a high speed transmission line, in one rack. Here, a “track”is a case which houses electronic boards constituting a terminalmultiplexer, and is provided with printed circuits connecting betweenelectronic boards. A rack is limited in its size from the viewpoint ofhandling requirements such as transportation and installation. Thus,when a terminal multiplexer can not be constructed with single rack butwith a plurality of racks, signals should be sent and received among theracks. To send and receive signals among the racks, cables should beused instead of printed circuit on an electronic board. Accordingly, andfor other reasons, there are some limitations in terms of number andspeed of signals, differently from sending and receipt of signals withina rack. Thus, for example, it is difficult to employ such aconfiguration that, in LTE etc. of 1:n configurations, n working highspeed transmission lines and one protection high speed transmission lineare connected to inputs of a single selector, and that selector switchesthe above-described working and protection lines.

SUMMARY OF THE INVENTION

A first object of the present invention is to provide a method ofconstructing a terminal multiplexer, by which a configuration of atransmission system can be changed by upgrading terminal multiplexerssuch as LTEs or ADMs used in a conventional transmission system.

A second object of the present invention is to provide a terminalmultiplexer having a configuration suited for using a plurality of racksto construct a terminal multiplexer.

To accomplish the above-described first object, the present inventionprovides a method of constructing a terminal multiplexer, comprisessteps of providing a high speed transmission line interface unitresponsible for signal input-output interface with a set of sending andreceiving high speed transmission lines; a low speed transmission lineinterface unit responsible for signal input-output interface with a setof sending and receiving low speed transmission lines; a multiplexconverting unit for performing multiplexing and demultiplexing betweenhigh speed signals transmitted on the high speed transmission lines andlow speed signals transmitted on the low speed transmission lines; and aswitching unit for performing switching between the high speed signalstransmitted on the high speed transmission lines and the low speedsignals transmitted on the low speed transmission lines, which has aninterface for signals outside of the unit, which is made common with aninterface for signals outside of the multiplex converting unit;

combining the high speed transmission line interface unit, and themultiplex converting unit, the low speed transmission line interfaceunit to construct a terminal multiplexer; and

constructing a channel rearrange equipment by substituting the switchingunit for the multiplex converting unit of the terminal multiplexer.

According to such a construction method, a terminal multiplexer such asLTE can be upgraded to a channel rearrange equipment such as ADM, simplyby substituting a switching unit for a terminal multiplexer. Thus, bysuch upgrading, the configuration of a transmission system can bechanged.

Further, to accomplish the above-described second object, the presentinvention provides a terminal multiplexer for transmitting signals to anapparatus at each side to be connected to the terminal multiplexer,using, for example, n (n is an integer greater than or equal to 1) setsof working high speed transmission lines and one set of sending andreceiving protection high speed transmission lines, comprising:

n working equipments, i.e. 1st to n-th working equipments and oneprotection equipment; wherein each of the working equipments comprises:a high speed transmission line interface unit responsible for signalinput-output interface with a set of working high speed transmissionlines;

a plurality of low speed transmission line interface units responsiblefor signal input-output interface with a set of sending and receivinglow speed transmission lines;

a multiplex converting unit which performs demultiplexing of high speedsignals received by the high speed transmission line interface unit fromthe working high speed transmission lines, to distribute thedemultiplexed signals to respective the low speed transmission lineinterface units as signals to be sent to the low speed transmissionlines, and performs multiplexing of low speed signals received by therespective low speed transmission line interface units from low speedtransmission lines, to send the multiplexed signals to the high speedtransmission line interface unit as high speed signals to be sent to theworking high speed transmission lines, and

a first forwarding unit connected to the multiplex converting unit;

the protection equipment comprising at least:

a high speed transmission line interface unit responsible for signalinput-output interface with a set of protection high speed transmissionlines; and

a second forwarding unit connected to the high speed transmission lineinterface unit;

the second forwarding unit of the protection equipment being connectedto the first forwarding unit of the first working equipment;

the first forwarding unit of the m-th (m is an integer varying from 1 to(n−1)) working equipment being connected to the first forwarding unit ofthe (m+1)-th working equipment; and

the first forwarding units of the working equipments and the secondforwarding unit of the protection equipment forming a transmissionsystem which forwards high speed signals received by the high speedtransmission line interface unit of the protection high speedtransmission lines from the protection high speed transmission lines, toa multiplex converting unit of any working equipment successively, ashigh speed signals to be objects of demultiplexing in the multiplexconverting unit in question instead of high speed signals received bythe high speed transmission line interface unit, and forwarding(sending) high speed signals multiplexed by the multiplex convertingunit of any working equipment to the high speed transmission lineinterface unit of the protection equipment as high speed signals to besent from the protection high speed transmission lines.

According to a terminal multiplexer constructed as such a terminalmultiplexer, by forwarding high speed signals which should be sent to orreceived from protection high speed transmission lines, successivelybetween forwarding units of the working equipments and protectionequipment, it is possible to extend the protection high speedtransmission lines as substitutes of a faulty working high speedtransmission line up to a multiplex converting unit of a workingequipment connected to the faulty working high speed transmission line.Thus, capacity corresponding to the transmission capacity of theprotection high speed transmission line is sufficient as the capacity ofsignal line needed for connection between the working equipments and theprotection equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing construction of a rack used for a terminalmultiplexer;

FIG. 2A is a block diagram showing construction of LTE in 1:1configuration;

FIG. 2B is a view showing a state in which units of the LTE of FIG. 2Aare mounted in a rack;

FIG. 3A is a block diagram showing construction of ADM applied for2-Fiber UPSR/BLSR;

FIG. 3B is a view showing a state in which units of the ADM of FIG. 3Aare mounted in a rack;

FIG. 4A is a block diagram showing construction of an LTE in 1:nconfiguration;

FIG. 4B is a view showing a state in which units of the LTE of FIG. 4Aare mounted in racks;

FIG. 5A is a block diagram showing another construction of an LTE in 1:nconfiguration;

FIG. 5B is a view showing a state in which units of the LTE of FIG. 5Aare mounted in racks;

FIG. 6A is a block diagram showing construction of an ADM applied for4-Fiber BLSR;

FIG. 6B is a view showing a state in which units of the ADM of FIG. 6Aare mounted in racks;

FIG. 7 is a block diagram showing construction of an ADM in 1:1 linearconfiguration;

FIG. 8 is a block diagram showing construction of an ADM in 1:n linearconfiguration;

FIG. 9A is a block diagram showing construction of an SELH unit;

FIG. 9B is a block diagram showing construction of an SELH(P) unit;

FIG. 10 is a schematic view showing construction of a circuit whichperforms switching of time slots using memory;

Fig. 11 is a schematic view showing construction of a delay circuit;

FIG. 12 is a block diagram showing a unit which can be used commonly asan SELH unit and an SELH(P) unit;

FIG. 13A is a view showing basic construction of a transmission systemusing an LTE;

FIG. 13B is a view illustrating switch from working lines to protectionlines;

FIG. 13C is a view illustrating another example of switching fromworking lines to protection lines;

FIG. 14A is a view showing construction of a transmission system usingan ADM;

FIG. 14B is a view showing construction of a transmission system inwhich a plurality of ADMs are connected linearly;

FIG. 14C is a view showing construction of a transmission system inwhich a plurality of ADMs are connected in a ring shape;

FIG. 15A is a view illustrating switching from working high speedtransmission lines to protection high speed transmission lines by LTEsin 1:1 configuration;

FIG. 15B is a view illustrating switching from working high speedtransmission lines to protection high speed transmission lines by LTEsin 1:n configuration;

FIG. 16A is a view showing basic construction of a 4-Fiber BLSRtransmission system;

FIG. 16B is a view illustrating switching from working high speedtransmission lines to protection high speed transmission lines in4-Fiber BLSR;

FIG. 16C is a view illustrating another example of switching fromworking high speed transmission lines to protection high speedtransmission lines in 4-Fiber BLSR;

FIG. 17A is a view showing basic construction of a transmission systemof 2-Fiber UPSR or 2-Fiber BLSR;

FIG. 17B is a view illustrating switching from working slots toprotection slots on high speed transmission lines in 2-Fiber UPSR or2-Fiber BLSR; and

FIG. 17C is a view illustrating another example of switching fromworking high speed transmission lines to protection high speedtransmission lines in 2-Fiber UPSR or 2-Fiber BLSR.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Now, an embodiment of the present invention will be described.

In the present embodiment, there are provided 8 kinds of unit: a 10Ginterface which sends and receives signals to or from an optical fibertransmission line for optical/electrical and electrical/opticalconversion, for example; SOH for overhead processing of signals; SELH, aselector on the side of the high speed signals; SELH(P), a selector onthe side of the high speed signals; SWH, a switch on the side of thehigh speed signals; SWL, a switch on the side of the low speed signals;PINF for sending and receiving signals between racks; and SELL, aselector on the side of the low speed signals for selection of signalsbetween low speed transmission lines, and one or more kinds of LINFresponsible for interface with low speed transmission lines. Bycombining these units, terminal multiplexers such as LTE or ADM adaptedfor various configurations of transmission system are constructed. Eachunit comprises one or more electronic boards mounted in a rack.

Further, 10G interface and SOH together make a high speed interfaceundertaking interface with the optical fiber transmission line.Accordingly, 10G interface and SOH may be treated as one high speedinterface unit.

Further, as shown in FIG. 1, in the present embodiment, the terminalmultiplexer is constructed by using a rack having 5 slots. When electricboards are mounted into the rack, they are connected by wiring providedin the rack. In the following description of the present embodiment,respective slots are referred to as COM, HS1, HS2, LS1 and LS2.

Into the slot COM, there is mounted an electronic board bearing variouscontrol systems which perform clock generation, power control, systemswitching control, maintenance control, and the like.

First, FIGS. 2A and 2B show LTEs connected in point-to-point manner in a1:1 configuration.

As shown in FIG. 2A, in this case, the LTE comprises two 10G interfaceunits 10 a, 10 b, two SOH units 20 a, 20 b, two duplicated SELH units 30a, 30 b, plural sets of duplicated SELL units 40 a, 40 b, and pluralsets of duplicated LIF units 50 a, 50 b. Further, FIG. 2B shows slots ofa rack into which respective units are mounted.

In an LTE having such construction, at the time of normal operation,optical signals are received by working (W) 10G interface 10 a fromworking optical fiber transmission line 100 a which transmits signals ata transmission speed of 10G, and, after being converted into electricalsignals, they are sent to working SOH 20 a, subjected to given overheadprocessing, and sent to working SELH 30 a. These signals are sentthrough working SELH 30 a to working SELL 40 a, and demultiplexed there.Then, signals in respective time slots are sent to respective workingLIF 50 a in accordance with the destinations of the signals. Each LIF 50a converts the received signals to low speed signals and sends them tolow speed transmission line 300.

Conversely, signals received by respective working LIFs 50 a from lowspeed transmission lines 300 are subject to time division multiplexingat working SELL 40 a, sent to working SELH 30 a and then to both theworking SOH 20 a and the protection SOH 20 b, and there subjected to theoverhead processing. Then, the signals are sent to the working 10Ginterface unit 10 a and the protection 10G interface unit 10 b,converted to optical signals, and sent respectively to working opticalfiber transmission line 100 b and protection optical fiber transmissionline 200 b on the sending side. Namely, the working and protectionoptical fiber transmission lines 100 b, 200 b on the sending side aresent the same signals which are converted from the signals received fromthe low speed transmission lines by time division multiplexing. Thus, infact, even at the time of normal operation, each LTE receives the samesignals from the working optical fiber transmission line 100 a and theprotection optical fiber transmission line 200 a. Further, the signalsare subject to the overhead processing at protection SOH 20 b, andinputted into working and protection SELHs.

Now, in such a construction, when a problem arises in some workingoptical fiber transmission line, the LTE receiving signals from theoptical fiber transmission line in question performs the followingswitching processing.

Namely, substituting for signals received from working SOH 20 a, workingSELH 30 a selects signals received from protection SOH 20 b, and sendsthem to working SELL 40 a. Protection SELH 30 b performs the sameoperation. As described above, the same signals are received from theworking optical fiber transmission line 100 a and from the protectionoptical fiber transmission line 200 a, and the above operation completesswitching from the working lines to the protection lines as describedabove referring to FIG. 13B.

Next, there will be described upgrading of such an LTE in a 1;1configuration to ADM of 2-Fiber BLSR or ADM of 2-Fiber UPSR.

Here, ADM of 2-Fiber BLSR and ADM of 2-Fiber UPSR can be realized withthe same construction. FIG. 3A shows the construction of ADM, and FIG.3B shows a rack into which units are mounted.

As will be understood from FIGS. 3A and 3B, upgrading to ADM in thiscase can be realized by changing the two duplicated SELHs 30 a, 30 b inthe construction of LTE shown in FIG. 2A into duplicated two SWHs 60 a,60 b, and by changing two duplicated SELLs 40 a, 40 b in theconstruction of LTE into two duplicated SWLs 70 a, 70 b. Here, SELH andSWH are made to be common in the interface of signal lines with therack, and, accordingly, they can be exchanged by removing an electronicboard constituting SELH from the rack and mounting an electronic boardconstituting SWH into the rack.

Now, operation of ADM of 2-Fiber UPSR will be described.

It is assumed that an optical fiber transmission line 110 a on the Westside and an optical fiber transmission line 120 a on the East side areworking, and an optical fiber transmission line 110 b on the West sideand an optical fiber transmission line 120 b on the East side areprotection. At the time of normal operation, signals in respective timeslots inputted from the optical fiber transmission line 110 a on theWest side are inputted through 10G interface 10 a and SOH 20 a to SWH 60a, and switched there to SWL 70 a and SOH 20 b in accordance withdestinations of signals of respective time slots. Signals sent to SWL 70a are switched to respective LIFs 50 a. Signals from LIFs 50 a areinputted through SWL 70 a to SWH 60 a, and switched there to SOHs 20 a,20 b. Further, to SWH 60 a, there are inputted signals from the opticalfiber transmission line 120 b through 10G interface 10 b and SOH 20 b,and SWH 60 a switches signals in respective time slots to SOH 20 b inaccordance with their destinations. The signals switched from SWH 60 ato SOHs 20 a, 20 b, are sent to 10G interfaces 10 a, 10 b, and to theoptical fiber transmission lines 110 b, 120 a, respectively.

In such a construction, there may arise such a problem that, forexample, signals from ADM located on the upstream side of the faultypoint with respect to signal flow on a ring formed by working opticalfiber transmission lines can not be received from the optical fibertransmission line 110 a on the West side. In that case, as for signalsfrom ADM located upstream from the faulty point, SWH 60 a of ADMswitches signals received from SOH 20 b to SWL, instead of signalsreceived from SOH 20 a.

When each ADM performs such an operation, the automatic protectionswitching shown in FIG. 17C can be realized.

Next, there will be described operation of ADM having the constructionof FIG. 3A in the case of 2-Fiber BLSR.

To clarify signal flows between transmission lines, description isfocused on the relation of operation of SWH 60 a with signal flowsbetween transmission lines, without referring to operations of otherparts. At the time of normal operation, in ADM, signals inputted fromthe optical fiber transmission lines 110 a, 120 b on the receiving sideon both West and East sides are inputted to SWH 60 a. Among the receivedsignals, signals in the working time slots are switched by SWH 60 a toworking time slots of the low speed transmission lines or of the opticalfiber transmission lines 110 b, 120 a. Signals inputted from the lowspeed transmission lines are switched by SWH 60 a to the working timeslots of the optical fiber transmission lines 110 b, 120 a. Further,signals in protection time slots inputted from the optical fibertransmission lines on the receiving side on both West and East sides aretransited (forwarded) by SWH 60 a to protection time slots of theoptical fiber transmission lines 110 b, 120 a, 120 b, 110 a on the otherside.

On the other hand, at the time of automatic protection switching, in twoADMs adjacent to a faulty working optical fiber transmission line, SWH60 a stops transiting (forwarding) signals between the protection timeslots, and switches signals which have been switched to working timeslots of the faulty working optical fiber transmission line, toprotection time slots of an optical fiber transmission line transmittingsignals from the ADM in question in the opposite direction to thetroubled working optical fiber transmission line. Further, instead ofthe signals received from the working time slots of the faulty workingoptical fiber transmission line, signals received from protection timeslots of an optical fiber transmission line transmitting signals to theADM in question in the opposite direction to the faulty working opticalfiber transmission line, become objects of switching to the low speedtransmission lines and the working time slots of the optical fibertransmission line transmitting signals from the ADM in question in theopposite direction to the faulty working optical transmission line.

The above-described operation realizes the switching operation at thetime of the automatic protection switching shown in FIG. 17B.

Next, there will be described upgrading of LTE in 1:1 configurationshown in FIG. 2A to LTE in 1:n configuration.

FIG. 4A shows construction of LTE in 1:n configuration, and FIG. 4Bshows racks into which units are mounted.

As shown in the figures, in this case, LTE comprises one rack forprotection processing, connected with protection optical fibertransmission lines 200 a and 200 b, and n racks for working processing,connected with working optical fiber transmission lines 100 a, 100 b,110 a, 110 b, . . . , lnOa, lnOb respectively.

Each rack constitutes a bay as a functional unit of LTE in 1:nconfiguration. Each of n bays for working processing 310, 320, . . . hassuch a construction that, in LTE in 1:1 configuration shown in FIG. 1,the protection 10G interface 10 b has been removed, and PINF 80 has beensubstituted for the protection SOH 20 b. The bay 300 for protectionprocessing has such a construction that, in the rack for workingprocessing, two duplicated SELH have been replaced by two duplicatedSELH(P) 90.

Here, an electronic board constituting each SOH 20 and an electronicboard constituting each PIN 80 are common in their signal interface witha rack, and thus, an electronic board constituting SOH 20 and anelectronic board constituting PINF 80 can be exchanged by removing theformer from the rack and mounting the latter into the rack. Further, anelectronic board constituting each SELH 30 and an electronic boardconstituting each SELH(P) 90 are common in their signal interface with arack, and thus, an electronic board constituting SELH 30 and anelectronic board constituting SELH(P) 90 can be exchanged by removingthe former from the rack and mounting the latter into the rack. In thepresent embodiment, LTE in 1:1 configuration can be upgraded to LET in1:n configuration, by upgrading the LTE in 1:1 configuration to one ofbays for working processing, and newly introducing the other baysconstituting LTE in 1:n configuration.

At the time of normal operation, each bay for working processing in LTEof FIG. 4A operates similarly to the above-described operation of LTE in1:1 configuration, each performing multiplex conversion between workingoptical fiber transmission lines connected thereto and low speedtransmission lines connected thereto, However, in LTE in 1:nconfiguration, at the time of normal operation, signals are not sent tothe protection optical transmission lines 200 a, 200 b.

Next, there will be described such a case that, where a problem hasarisen, for example, in an optical transmission line 110 a connected toa working bay 320 on the receiving side. In this case, SELH(P) 90 of thebay 300 for protection processing sends signals received from aprotection optical fiber transmission line 200 b through 10G interface10 and SOH 20 to PINF 80. Those signals are converted to low speedsignals, for example, each having a rate of 150M, and thereafter aresent, through optical interconnect connecting racks, to PINF 80 of a bay310. PINF 80 of the bay 310 transits the signals received from the bay300 to PINF 80 of the bay 320. PINF 80 of the bay 320 sends the signalsreceived from the bay 310 to SELH 30. SELH 30 of the bay 320 selects thesignals received from PINF 80 instead of the signals from SOH 20, andsends the selected signals to SELL 40.

Conversely, when a problem arises in an optical fiber transmission line120 b connected to the working bay 320 on the sending side, SELH 30 ofthe bay 330 sends signals to PINF 80 instead of SOH 20. On receiving thesignals, PINF 80 sends them to PINF 80 of the bay 310. PINF 80 of thebay 310 transits the signals received from the bay 320 to the bay 300.On receiving the signals, PINF 80 of the bay 300 converts them to serialsignals, and sends them SELH(P) 90. SELH(P) 90 sends the signalsreceived from PINF 80 to SOH 20. The signals are sent through theprotection optical fiber transmission line 200 b.

Thus, in this construction, PINF 80 extends the Protection opticaltransmission line to the working bay connected to the faulty workingoptical fiber transmission line.

The above-described operation is performed by LTEs at both ends of thefaulty working optical fiber transmission line, thus realizing theuni-directional switching of FIG. 13B.

Further, the bi-directional switching of FIG. 18C is realized by thesame operation as the uni-directional switching in the case of bothsending and receiving optical fiber transmission lines being faulty.

Alternatively, the bi-directional switching may be realized byconnecting respective PINFs 80 of the bays in a ring shape as shown inFIGS. 5A and 5B.

In this construction, extension by PINFs 80 of a protection opticalfiber transmission line on the receiving side to a working bay connectedto a faulty working optical transmission line, and extension by PINFs 80of a protection optical fiber transmission line on the sending side tothe working bay connected to the faulty working optical transmissionline are realized through different routes. For example, as shown in thefigures, extension of a protection optical fiber transmission line 200 aon the receiving side to the bay 320 is attained through PINFs 80 of thebays 300, 310, while extension of a protection optical fibertransmission line 200 b on the sending side to the bay 320 is attainedthrough PINFs 80 of the bays 320, 330, . . . , 3n0, and 300.

An advantage of employing this ring-shape construction is that theamount of hardware can be kept to a low level because for example, thenumber of signal lines connecting racks is small.

Next, there will be described upgrading ADM of 2-Fiber BLSR and ADM of2-Fiber UPSR shown in FIGS. 3A and 3B to ADM of 4-Fiber BLSR.

FIG. 6A shows construction of ADM in this case, and FIG. 6B shows racksinto which units are mounted.

As shown in the figures, ADM in this case comprises a rack for workingprocessing, connected with working optical fiber transmission lines 110a, 110 b, 120 a and 120 b, and a rack for protection processing,connected with protection optical fiber transmission lines 200 a, 200 b,210 a and 210 b. Bays corresponding to respective racks have the sameconstruction as ADM of 2-Fiber BLSR and ADM of 2-Fiber UPSR shown inFIG. 3A. Accordingly, in this case, upgrading can be performed byletting the existing ADM of 2-Fiber BLSR or 2-Fiber UPSR be one bay ofADM of 4-Fiber BLSR, introducing a new bay having the same construction,and connecting SWHs 60 a, 60 b of both ADM with optical interconnects.As LTE in 1:1 configuration can be upgraded to ADM of 2-Fiber BLSR or2-Fiber UPSR, LTE in 1:1 configuration, can of course also be upgrade toADM 4-Fiber BLSR.

Now, operation of ADM of FIGS. 6A and 6B will be described.

To clarify signal flows between transmission lines, description isfocused on the relation of operation of SWH 60 a with signal flowsbetween transmission lines, without referring to operations of otherparts. At the time of normal operation, in a working bay 400, signalsreceived from optical fiber transmission lines on the receiving side onthe West and East sides are inputted into SWH 60 a. SWH 60 a switchesthe received signals in respective time slots to low speed transmissionlines or to time slots of optical fiber transmission lines on the otherside 110 b, 120 a. Further, signals received from the low speedtransmission lines are switched by SWH 60 a to time slots of the opticalfiber transmission lines 110 b, 120 a.

Further, SWH 60 a of a bay 410 or protection processing forwards signalsreceived from an optical fiber transmission line 200 a to an opticalfiber transmission line 210 a as they are, and forwards signals receivedfrom an optical fiber transmission line 210 b to an optical fibertransmission line 200 b as they are.

At the time of automatic protection switching, when, for example, aproblem arises in the working optical fiber transmission lines 120 a,120 b on the East side, SWH 60 a of the bay 400 for working processingsends signals which has been switched to the working optical fibertransmission line 120 a, to SWH 60 a of the bay 410 for protectionprocessing. Further, instead of signals which have been received fromthe working optical transmission line 120 b, signals received from thebay 410 for protection processing is made an object of switching. On theother hand, when, SWH 60 a of the bay 410 for protection processingstops the forwarding operation between the above-described protectionoptical fiber transmission lines and performs the switching operationshown in FIG. 16B, it switches the signals received from the bay 400 tothe optical fiber transmission line 200 b, and sends signals receivedfrom the optical fiber transmission line 200 a to SWH 60 of the bay 400.Further, when SWH 60 a of the bay 410 for protection processing stopsthe forwarding operation between the above-described protection opticalfiber transmission lines and performs the switching operation shown inFIG. 16C, it switches the signals received from the bay 400 to theoptical fiber transmission line 210 a and sends signals received fromthe optical fiber transmission line 210 b to SWH 60 of the bay 400.

The above described operation is performed by ADMs adjacent to thetroubled portion, realizing the automatic protection switching shown inFIGS. 16B, 16C,

Next, there will be described upgrading of ADM of 2-Fiber BLSR or ADM of2-Fiber UPSR shown in FIG. 8A to ADM in 1:1 linear configuration.

FIG. 7 shows construction of ADM in this case.

As shown in the figure, ADM in this case has the same construction asADM of 4-Fiber BLSR shown in FIG. 6A. Accordingly, upgrading can beperformed by exchanging similar units. Further, as described above, thepresent construction can also be obtained by upgrading LTE in 1:1configuration.

Further, its operation at the time of normal operation is the same as4-Fiber BLSR. Its operation at the time of the automatic protectionswitching as shown in FIG. 15B is same as the case of the switchingoperation shown in FIG. 16B.

Last, there will be described upgrading to ADM in 1:n linearconfiguration.

FIG. 8 shows construction of ADM in this case.

As shown, in this case, ADM has such a construction that there areprovided (1+n) sets of bays 800-80n, one set as a protection bay set andn sets as working bay sets, with each set comprising East bay 810 andWest bay 811. East bay 810 is obtained, in one of the racks constitutingADM in 1:1 linear configuration shown in FIG. 7, by removing two 10Ginterfaces 10 a, 10 b, and replacing two SOHs 20 a, 20 b with two PINFs80 a, 80. West bay 811 is the remaining rack of FIG. 7, and PINFs 80 a,80 b of respective bay sets are successively connected in a chain sothat protection bay set 800 is located at the end.

Accordingly, one of plural bay sets of ADM can be constructed by usingADM in 1:1 linear configuration. Further, as can be seen from FIG. 8,each East bay has such a construction that 10G interface of each bay ofLTE in 1:n configuration is removed, SELH is replaced with SWH, SOH withPINF, and SELL with SWL, and introduced PINFs are connectedsuccessively. Accordingly, ADM in 1:n linear configuration can beobtained by upgrading LTE in 1:n configuration.

The protection bay set 800 is connected with one sending and onereceiving protection optical fiber transmission lines for each of theEast and West sides. Each of n working bay sets 801-80 n is connectedwith one sending and one receiving working optical fiber transmissionlines for each of the East and West sides.

At the time of normal operation, the West bay of each working bay set801-80 n operates similarly to the above-described operation of theworking bay of ADM in 1:1 linear configuration, realizing transmissionbetween ADMs or between ADM and LTE using n working transmission lines.

On the other hand, at the time of automatic protection switching, when,for example, a problem arises in the optical fiber transmission line onthe West side of the second working bay set, as in the above-describedcase of LTE in 1:n configuration, protection optical fiber transmissionline on the West side is extended to SWH of the West bay of secondworking bay set, by transmitting signals through 10G interface, SOH andSWH of the West bay of the protection bay set; SWH and PINF of the Eastbay of the protection bay set; PINF of the East bay of the first workingbay set; working PINF and SWH of the East bay of the second working bayset; and SWH of the West bay of the second working bay set, in thisorder. That extended protection optical fiber transmission line is usedby SWH of the West bay of the second working bay set, instead of thefaulty optical fiber transmission line on the West side.

Such an operation is performed by ADMs located on both ends of thefaulty optical fiber transmission line, realizing switching from theworking optical fiber transmission line to the protection optical fibertransmission line.

Alternatively, bay sets of Fig, 8 may be connected in a ring shape as inthe LTE in 1:n configuration shown in FIG. 5A, and extension of theprotection optical fiber transmission line may be realized in such amanner that signals are forwarded only in one rotational direction onthe ring. For example, when a problem arises in the optical fibertransmission line on the West side of second working bay set, similarlyto the above-described case of LTE in 1:n configuration, the receivingprotection optical fiber transmission line on the West side is extendedto SWH of West bay of the second working bay set, by forwarding signalsthrough 10G interface, SOH and SWH of the West bay of the protection bayset; SWH and PINF of the East bay of the protection bay set; PINF of theEast bay of the first working bay set; working PINF and SWH of the Eastbay of second working bay set; and SWH of the West bay of second workingbay set, in this order. Further, the sending protection optical fibertransmission line on the West side is extended to working SWH of theWest bay of the second working bay set, by transiting signals throughworking SWH of the West bay of the second working bay set; working SWHand PINF of the East bay of the second working bay set; working PINF ofthe East bay of the third working bay set; . . . ; working PINF of theEast bay of the n-th working bay set; PINF and SWH of the East bay ofthe protection bay set; and SWH, SOH and 10G interface of the West bayof the protection bay set, in this order.

As described above, according to the present invention, it is possibleto upgrade a terminal multiplexer, utilizing the constructions of theexisting terminal multiplexers. Further, as has been described, eachconstruction of the units of LTE in 1:1 configuration and ADM of 2-FiberBLSR/2-Fiber UPSR is a duplicated one. Accordingly, at the time ofupgrading, necessary units may be exchanged in one of the twin systemsat once, and the other system may be used during the exchange, so thatthe transmission system may be operated continuously.

However, if a difference in delay times exists between input and outputsignals for SELH, SELH(P) and SWH due to processing in SELH, SELH(P) andSWH, problems may be caused such as loss and duplication of signals atthe time of switching of the system in operation.

Accordingly, in the present embodiment, SELH is constructed as shown inFIG. 9A, and SELH(P) as shown in FIG. 9B so that delay times are made tocoincide in these units.

Here, switching of signals in time slots as in SWH is performed, asshown in FIG. 10, by means of memory 900, write circuit 901 whichsequentially writes signals in each time slot coming in and out, andread circuit 902 which reads signals in each time slot from the memoryin order set by a controller (not shown). Accordingly, a delay time isusually produced which is larger than the time corresponding to thenumber of time slots. This delay time is generally larger than a delaytime in a selector which performs a selection operation, such as SELHand SELH(P).

In the present invention, delay circuit 1300 is provided for SELH andSELH(P) for adjusting the delay time of signals. As shown in FIG. 11,the delay circuit 300 comprises a sequential counter 302 whichsequentially generates addresses in memory 301 for writing signals ineach time slot coming in and out, and a decoder 303 which obtains readaddress by adding a count value of the sequential counter 302 and anoffset corresponding to an adjust time desired. According to such andelay circuit 1300, time elapsing between writing and reading signals toand from the memory 301 can be adjusted by suitably setting the offsetvalue added by the decoder 303.

In FIG. 9A, the reference numeral 320 denotes a selector which selectssignals sent from working SOH or signals sent from protection SOH orPINF, and sends the selected signal to SELL.

Further, in FIG. 9B, the reference numeral 320 shows a selector forsending signals sent from PINF to a protection optical fibertransmission line.

As SELH and SELH(P) shown in FIGS. 9A and 9B, a unit provided with threeselectors 1301, 1302, 1303, as shown in FIG. 12, may be used in common.In this case, when it is used as SELH(P), selections in the selectors1301, 1302 are fixed to form the same signal flow as in FIG. 9B, andwhen used as SELH, selections in the selectors 1302, 1303 are fixed toform the same signal flow as in FIG. 9A.

Further, as a construction of an interface frame of an optical fibertransmission line related to the present embodiment, there may be usedSONET synchromous Optical network OC-N frame construction having atransmission rate of 51.84 Mb/s or a multiple thereof, or STM-N frameconstruction in SDH hierarchy regulated in ITU Recommendation having atransmission rate of 155.52 Mb/s or a multiple thereof.

As described above, according to the present embodiment, a terminalmultiplexer can be upgraded using the existing terminal multiplexer, andconstruction of a transmission system can be changed by that upgrading.

Further, as in the above-described case of LTE in 1:n configuration, aterminal multiplexer can be constituted by a plurality of racks, and,when working and protection systems are switched, the capacity ofsignals which are required to be sent and received between racks can bemade to be lower in level. Thus, the present construction is suitablefor constructing a terminal multiplexer using a plurality of racks.

What is claimed is:
 1. A method of constructing a channel rearrangeequipment, comprising steps of: providing first and second sets ofelements, each set of elements including: a high speed transmission lineinterface unit responsible for signal input-output interface with a setof sending and receiving high speed transmission lines, said signalinput-output interface being duplicated a west and east side ports; alow speed transmission line interface unit responsible for signalinput-output with a set of sending and receiving low speed transmissionlines; and a switching unit for switching between the high speed signalstransmitted on the high speed transmission lines and the low speedsignals transmitted on the low speed transmission lines; andinterconnecting said first and second sets of elements with each othersuch that the west and east side ports of said high speed transmissionline interface unit of said first set of elements are used as a workinghigh speed transmission line and the west and east side ports of saidhigh speed transmission line interface unit of said second set ofelements are used as a protection high speed transmission line.
 2. Themethod of claim 1, wherein said switching unit is connected by means ofan optical transmission medium.
 3. A method of constructing a terminalmultiplexer, comprising steps of: providing a high speed transmissionline interface unit responsible for signal input-output interface with aset of sending and receiving high speed transmission lines; a low speedtransmission line interface unit responsible for signal input-outputinterface with a set of sending and receiving low speed transmissionlines; a multiplex converting unit for performing multiplexing anddemultiplexing between high speed signals transmitted on the high speedtransmission lines and low speed signals transmitted on the low speedtransmission lines, and providing a plurality of different electroniccircuit boards for said low speed transmission line interface unit,which have a common interface of signals inside said low speedtransmission line interface such that said plurality of electroniccircuit boards are interchangeable with one another to change a frameconfiguration of said low speed transmission interface.
 4. The method ofclaim 3, wherein an interface frame construction used for transmittingsignals in said set of low speed transmission lines is a SONET OC-Nframe construction having a transmission rate of 51.84 Mb/s or amultiple of said 51.84 Mb/s.
 5. The method of claim 3, wherein aninterface frame construction used for transmitting signals in said setof low speed transmission lines is a STM-N frame construction in SDHhierarchy conforming to IDU Recommendations, having a transmission rateof 155.52 Mb/s or a multiple of said 155.52 Mhb/s.
 6. A channelrearrange equipment, comprising: first and second sets of elements, eachset of elements including: a high speed transmission line interfaceresponsible for signal input-output interface with a set of sending andreceiving high speed transmission lines; a low speed transmission lineinterface responsible for signal input-output interface with a set ofsending and receiving low speed transmission lines; and a switching unitfor switching between high speed signals transmitted on the high speedtransmission lines and low speed signals transmitted on the low speedtransmission lines, wherein the switching units of said first and secondsets of elements are interconnected, the high speed transmission lineinterface of one of said first and second sets of elements is used as aworking high speed transmission line, and the high speed transmissionline interface of the other one of said first and second sets ofelements is used as a protection high speed transmission line.
 7. Thechannel rearrange equipment of claim 6, wherein an interface frameconstruction used for transmitting signals in said set of low speedtransmission lines is a SONET OC-N frame construction having atransmission rate of 51.84 Mb/s or a multiple of said 51.84 Mb/s.
 8. Thechannel rearrange equipment of claim 6, wherein an interface frameconstruction used for transmitting signals in said set of low speedtransmission lines is a STM-N frame construction in SDH hierarchyconforming to IDU Recommendations, having a transmission rate of 155.52Mb/s or a multiple of said 155.52 Mhb/s.